Some people abuse H1 tags by wrapping them around entire pages of content or by
using multiple H1 tags on a page.
This is a bad idea and borders on spam – the H1 tag should be used as a page
headline. It is perfectly legitimate to reduce the size of H1 text using a style sheet but
that’s about it. As a result, Google may be discounting H1 so it may carry less weight
for ranking moving forward.
The same can be said about image ALT text – some people put entire paragraphs of
content in them for each image on a page. It is perfectly legitimate to put keywords
relating to the image but that’s it. Similarly, image ALT text now carries less weight
than before. Images that are clickable (wrapped in a HREF link tag) do not appear to
have a discounting - yet.

Proper Internal Link Structure
Besides the title of a page, Google places special importance on the use of keywords
in the text of links. This means you need to structure your links correctly.

Ideally, you should only use text links on your site as opposed to graphical “button”
links. Google looks for keywords contained in link anchor text – the clickable portion
of the link. Google cannot see graphics-based links – all it has to go on is the ALT
attribute for image tags, which doesn’t carry as much weight.